Tech Stuff - Q.931 Information Elements

Information Elements (IEs) must appear in numerically ascending order within ascending codeset order. Not all IEs are valid with all message types. IEs take two formats; one-octet IEs or variable length IEs.

Codesets

The documentation defines four codesets being:

Codeset 0 -ITU standard (default start codeset)

Codeset 5 - National specific

Codeset 6 - Network Specific

Codeset 7 - User Specific

One-Octet IEs

These IEs are all shift types (escape codes in non-ITU language) between various code sets.

Value

Meaning

0x95

Locking Shift to Codeset 5

0x96

Locking Shift to Codeset 6

0x9D

Non-Locking Shift to Codeset 5

0x9E

Non-Locking Shift to Codeset 6

NOTE: Those of you still awake will have spotted that the top bit (bit 8 in ITU-speak) is always set on single octet IEs.

Variable Length ITU IEs (Codeset 0)

All the IEs shown are in 'C' type hexadecimal values rather than the more normal bit format of ITU documentation - for our ease of use. You are welcome to convert them back to binary if that is easier to work with!!

National Specific IEs (Codeset 5)

Since these message types are National they are listed under the country/region. These IE's are preceded with a locking (0x95) or non-locking (0x9D) shift to codeset 5.

North America - NI-1, 2 and 3

Value

Name

Notes

0x01

Operator System Access

Only in originating SETUP (User-Network)

0x2A

Display Text

Formatted text for display

Network Specific IEs (Codeset 6)

Since these message types are typically proprietary or National they are listed under the vendor (or country) value. These IE's are preceded with a locking (0x96) or non-locking (0x9E) shift to codeset 6.

North America - NI-1, 2 and 3

Value

Name

Notes

0x3E

Protocol Version Control

0x41

Closed User Group

0x42

Reverse Charging Indication

0x75

Redirecting Subaddress

0x7B

Call Appearance

Call Appearance number being used (Key system IE)

CUSTOM LUCENT

Value

Name

Notes

0x02

User Code

Provides authorization info for calls (voice or data)

0x21

Associated Type

Provides call status for key systems

0x22

Selected Call appearance

Network says use this call appearance

0x23

Origination Call Appearance

The call appearance we are using for this call

0x25

Destination Call Appearance

On incoming call - should be same as last SCA

0x26

Endpoint Identifier

0x32

Keypad Control

0x36

Switch hook

0 = on-hook, 1 = off-hook

0x37

Other Call Reference

Used in CONFerence operations

0x38

Feature Activation

two-octet format

0x39

Feature Indication

0x3A

Adjunct Control

0x3B

Display Control

0x3C

Display Field

5ESS is very verbose

0x7A

Management

used in MAN_INFO message types

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